This project is aimed at using long-range propagation of acoustic signals through at structure to detect changes induced by damage, cracking or flooding of hollow members. It is based on the idea that, if a change occurs within the structure, this will induce changes in acoustic signals transmitted between two points on it. These changes will only occur after a certain time in the history of the signal, and this time corresponds to the minimum travel time from the transmission point to the reception point via the point of damage. This minimum time will correspond to the fastesttravelling waves; under normal circumstances these are longitudinal compression waves. Thus if one is able to model the point-topoint transmission times of longitudinal compression waves through the structure, and one measures between sufficiently many points, it should be possible to locate damage by picking the times at which differences start to appear.
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